The most common method for testing the hardness of metal and other materials is Rockwell Hardness testing in which hardness of the material is measured by the depth to which it is penetrated under a specified load by the sphero-conical point of a mined natural diamond brazed to the end of a cylindrical metal shank.
The accuracy of the Rockwell testing procedure is dependent in part on the precision with which the conical point of the diamond penetrator or indenter conforms to a standardized shape. The prior standard required that the cone have an included angle of 120.degree. with a tolerance of plus or minus 30 minutes of angle, and currently this tolerance is tightened to 20 minutes for routine production testing, and to 6 minutes for standard laboratory testing. Further the newer standard has tightened the tolerance of the included angle of the diamond cone to plus or minus 20 minutes for indenters used in commercial testing, and to plus or minus 6 minutes for standard laboratory testing.
The standard limiting the 0.200 millimeter radius of the conical tip to a tolerance of plus or minus 0.002 millimeters has been tightened to plus or minus 0.001 millimeters for laboratory testing, although the tolerance for commercial testing remains unchanged.
An additional standard requires that the surface of the cone and the spherical tip shall blend in a truly tangential manner at 500X magnification.
To satisfy the above described standards it is necessary, as a practical matter, that a right, transverse conical section through the tip of the indenter does not deviate from perfect circularity by more than 25 microns in commercial indenters, nor more than 10 microns in laboratory indenters.
With prior indenters it has not been possible to meet the prior standards consistently, and the new standards are less likely to be met. Accordingly it is the object of the present invention to provide a diamond indenter which will not only meet but exceed current standards for Rockwell testing.